Multi-layer compensation film including stretchable barrier layers

ABSTRACT

A multilayer compensator has two or more first layers and one or more second layers. The overall in-plane retardation of the compensator is from 0 to 300 nm and the out-of-plane retardation is more negative than −20 nm or more positive than +20 nm. The compensator may be fabricated by: coating at least one barrier layer on at least one first layer; coating at least one second layer from an organic coating solvent on the barrier layer to produce an intermediate compensator structure; and stretching the intermediate compensator structure in at least one direction by between 1% and 60%. The barrier layer contains a polymer that is water soluble or water dispersible in an amount sufficient to impede the diffusion of the organic solvent between the other first layers and the second layers. All layers have been stretched simultaneously.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. non-provisional application Ser.No. 10/745,109, filed on 23 Dec. 2003 now U.S. Pat. No. 6,995,395.

FIELD OF THE INVENTION

The present invention relates to a multilayer optical compensator forliquid crystal displays. The invention also relates to a method formaking such a compensator and liquid crystal displays using thecompensator.

BACKGROUND OF THE INVENTION

Triacetylcellulose (TAC, also called cellulose triacetate) film hastraditionally been used by the photographic industry due to its uniquephysical properties and flame retardance. TAC film is also the preferredpolymer film for use as a cover sheet for the polarizers used in liquidcrystal displays. It is the preferred material for this use because ofits extremely low in-plane birefringence. Its out of plane birefringenceis also small (but not zero), and is useful in providing some opticalcompensation to the LCD.

Intrinsic birefringence describes the fundamental orientation of amaterial at a molecular level. It is directly related to the molecularstructure (bond angles, rotational freedom, presence of aromatic groups,etc.) of the material. The intrinsic birefringence is not affected byprocess conditions (temperature, stresses, pressures) used to make amacroscopic object.

Crystalline and liquid crystalline materials have the convenientproperty that their intrinsic birefringence manifests itself almostperfectly when they are assembled into a macroscopic article. Layers ofcrystalline and liquid crystalline molecules often can be manufacturedsuch that all the molecules in the article are in registry with eachother and thus preserve their fundamental orientation. The same is nottrue when making layers of an amorphous polymeric material. Theirintrinsic birefringence can be highly modified by the manufacturingprocess. Thus, the measured birefringence of an actual article will be aresultant of its intrinsic birefringence and the manufacturing process.Because in some embodiments we are dealing with such amorphous polymericmaterials, the following definitions refer to this measuredbirefringence and not intrinsic birefringence.

In-plane birefringence, Δn_(in), means the difference between n_(x) andn_(y), (n_(x)−n_(y)), where x and y lie in the plane of the layer, andwhere n_(x) and n_(y) are indices of refraction in the directions of xand y, respectively. Here, the x axis is taken as a direction of maximumindex of refraction in the x-y plane and the y direction isperpendicular to the x axis. Accordingly, n_(x) will be defined asalways being the larger refractive index, and n_(y) will be defined asthe being the smaller refractive index and in the y direction,perpendicular to n_(x). The sign convention used will be n_(x)−n_(y) andwill always be positive.

In-plane retardation, R_(in), is a quantity defined by (n_(x)−n_(y))d,where d is a thickness of the layer in the z-direction, perpendicular tothe x-y plane. R_(in) will always be a positive quantity. The values ofΔn_(in) and R_(in) hereafter are given at wavelength λ=590 nm.

Out of-plane retardation R_(th), of a layer is a quantity defined by[n_(z)−(n_(x)+n_(y))/2]d, where n_(z) is the index of refraction inz-direction. The quantity [n_(z)−(n_(x)+n_(y))/2] is referred to asout-of-plane birefringence, Δn_(th). If n_(z)>(n_(x)+n_(y))/2, Δn_(th)is positive, thus the corresponding R_(th) is also positive. Ifn_(x)<(n_(x)+n_(y))/2, Δn_(th) is negative and R_(th) is also negative.The values of Δn_(th) and R_(th) hereafter are given at λ=590 nm.

Amorphous means a lack of molecular order. Thus an amorphous polymerdoes not show molecular order as measured by techniques such as X-raydiffraction.

Chromophore means an atom or group of atoms that serve as a unit inlight adsorption. (Modern Molecular Photochemistry Nicholas J. TurroEditor, Benjamin/Cummings Publishing Co., Menlo Park, Calif. (1978) Pg77). Typical chromophore groups include vinyl, carbonyl, amide, imide,ester, carbonate, aromatic (i.e. heteroaromatic or carbocylic aromaticsuch as phenyl, naphthyl, biphenyl, thiophene, bisphenol), sulfone, andazo or combinations of these groups.

Non-visible chromophore means a chromophore that has an absorptionmaximum outside the range of 400–700 nm.

Continuous means that articles are in contact with each other. In twocontiguous layers, one layer is in direct contact with the other. Thus,if a polymer layer is formed on the substrate by coating, the substrateand the polymer layers are contiguous.

Synthetic polymer films (such as polycarbonate or polysulfone) are oftenused to enhance the minimal optical compensation that TAC provides.These synthetic polymers films are attached to the rest of the displayby adhesive lamination.

Generally in the field of optical materials, the synthetic polymer filmis used as an optically anisotropic film (having a high retardationvalue), while a TAC film is used as an optical isotropic film (having alow retardation value).

European Patent Application No. 0911656 A2 and Japanese PatentPublication 2000/275434 A both disclose a TAC film having highretardation. The TAC is used as a support for an optical compensatorsheet, which comprises the TAC support and an optically anisotropiclayer containing a discotic liquid crystal molecule. The TAC filmachieves high retardation by three methods (including the combination ofthese three methods): 1) the addition of special aromatic smallmolecules (i.e. triphenylene) to the TAC film, 2) cooling of the TACsolution before casting the film, and 3) stretching the TAC film. Theaddition of special aromatic molecules is discussed as being problematicas it can lead to “bleeding” of these molecules out of the TAC film.Also in the examples of this invention very long times (over an hour)are required to dry such TAC films. Such times would not be amenable toa roll to roll process.

In addition to the TAC film, the highly anisotropic, discotic liquidcrystal layer requires a special alignment technique and ultra violetradiation to crosslink this monomeric layer.

U.S. Published Patent Application 2001/0026338 A1 discloses a single TACfilm with high retardation without the highly anisotropic discoticlayer. This TAC film achieves high retardation by the incorporation ofmolecules with two or more aromatic groups into the TAC film followed bystretching of the TAC film. Without such stretching, this TAC film doesnot demonstrate any enhanced retardation compared to regular TAC. Withthis stretching both in and out of plane retardation are increased.These two orthogonal retardations cannot be independently controlled bythis method.

Japanese Published Patent Application JP1999-95208 describes a liquidcrystal display having an optical compensator (having high retardation)prepared by uniaxial stretching of a high polymer film. Such polymersinclude polyesters, polycarbonate, or polysulfone. This stretching stepis essential to obtain the desired optical properties. This stretchingaffects both in- and out-of-plane retardation simultaneously. These twoorthogonal retardations cannot be independently controlled by thismethod. Also, producing uniform optical compensators by this method isdescribed as being difficult.

This application also describes a compensator where the inventor uses anexfoliated inorganic clay material in a polymeric binder coated on topof a TAC support. The exfoliated inorganic clay material in this layeris the optically active material, not the polymeric binder.

Japanese Published Application JP2001-194668 describes a compensatormade by laminating polycarbonate films that have been stretched. Notonly does the approach require lamination (with its associateddifficulties), but it also requires two independent stretchings of twodifferent types of polycarbonate. The lamination step also requires thatthe two films be in registry with each other and that their optical axesbe orthogonal to each other.

U.S. Pat. Nos. 5,344,916, 5,480,964, and 5,580,950 describe compensationfilms for LDCs. However they do not mention the need for barrier layersto control curl and improve adhesion.

It is a problem to be solved to provide a multilayer optical compensatorthat is readily manufactured, that provides the required degree ofin-plane and out-of-plane compensation, that has excellent adhesionbetween layers and is free of curl caused by application of organicsolvent coating solutions.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a multilayer compensatorcomprises at least two polymeric first layers; and one or more polymericsecond layers. The first layers comprise a polymer having anout-of-plane birefringence not more negative than −0.005 and not morepositive than +0.005. The second layers comprise a polymer having anout-of-plane birefringence more negative than −0.005 or more positivethan +0.005. The overall magnitude of the in-plane retardation (R_(in))of the multilayer compensator is greater than 0 nm and less than 300 nmand the out-of-plane retardation (R_(th)) of the multilayer compensatoris more negative than −20 nm or more positive than +20 nm. One of thefirst layers is contiguous to a second layer and is between all of theother first layers and all of the second layers. At least one of thesecond layers is a layer coated from an organic solvent. The compensatorhas been stretched in at least one direction by at least 1% and not morethan 60% after at least two of the first were assembled together.Beneficially, the contiguous first layer includes a polymer that iswater soluble or water dispersible in an amount sufficient to limit anamount of the organic solvent that diffuses into the first layers to beless than 75 mg/ft² when the organic solvent is ethylacetate, less than105 mg/ft² when the organic solvent is propylacetate, and less than 150mg/ft² when the organic solvent is methylene chloride. Alsobeneficially, the polymer of the contiguous first layer is one selectedfrom the group consisting of polyurethanes, polyesters, polyesterionomers, epoxide containing acrylic copolymers, polyacrylates, andpolyvinyl alcohols.

In another aspect of the present invention, a multilayer compensatorcomprises at least two polymeric first layers; and one or more polymericsecond layers. The first layers comprise a polymer having anout-of-plane birefringence not more negative than −0.005 and not morepositive than +0.005. The second layers comprise a polymer having anout-of-plane birefringence more negative than −0.005 or more positivethan +0.005. The overall magnitude of the in-plane retardation (R_(in))of the multilayer compensator is greater than 0 nm and less than 300 nmand the out-of-plane retardation (R_(th)) of the multilayer compensatoris more negative than −20 nm or more positive than +20 nm. One of thefirst layers is contiguous to a second layer and is between all of theother first layers and all of the second layers. At least one of thesecond layers is a layer coated from an organic solvent. The contiguousfirst layer contains a polymer that is water soluble or waterdispersible in an amount sufficient to impede the diffusion of theorganic solvent between the other first layers and the second layers.All of the layers have been stretched simultaneously.

In yet another aspect of the invention, a method for forming acompensator polymeric film comprising two or more first layers having anout-of-plane birefringence not more negative than −0.005 and not morepositive than +0.005, and one or more second layers having anout-of-plane birefringence more negative than −0.005 or more positivethan +0.005, wherein the second layers comprise selected polymericmaterials having sufficient thickness so that the overall in-planeretardation (R_(in)) of the compensator is from 0 to 300 nm and theout-of-plane retardation (R_(th)) of the compensator is more negativethan −20 nm or more positive than +20 nm, comprises: (a) coating atleast one barrier layer on at least one first layer; (b) coating atleast one second layer from an organic coating solvent on the barrierlayer to produce an intermediate compensator structure; and (c)stretching the intermediate compensator structure in at least onedirection by at least 1% and not more than 60%. Beneficially, thebarrier layer contains a polymer that is applied from water and ispresent in an amount sufficient to limit an amount of the organicsolvent that diffuses into the first layers to be less than 75 mg/ft²when the organic solvent is ethylacetate, less than 105 mg/ft² when theorganic solvent is propylacetate, and less than 150 mg/ft² when theorganic solvent is methylene chloride. Also beneficially, the polymer ofthe contiguous first layer is one selected from the group consisting ofpolyurethanes, polyesters, polyester ionomers, epoxide containingacrylic copolymers, polyacrylates, and polyvinyl alcohols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a multi-layer compensator having 3layers.

FIG. 2 is a cross-sectional view of a multi-layer compensator having 4layers.

FIG. 3 is a cross-sectional view of a multi-layer compensator having 5layers.

FIG. 4 a is an exploded view of a liquid crystal display with onecompensating film.

FIG. 4 b is an exploded view of a liquid crystal display with twocompensating films.

DETAILED DESCRIPTION OF THE INVENTION

Commonly assigned U.S. patent applications: Ser. No. 10/745,109,entitled “MULTILAYER OPTICAL COMPENSATOR, LIQUID CRYSTAL DISPLAY, ANDPROCESS” and filed on 23 Dec. 2003 (“the '109 application”); Ser. No.11/165,090, entitled “MULTI-LAYERED COMPENSATION FILM USING SPECIFIED TgMATERIAL AS A BIREFRINGENT LAYER” and filed on the same date as thepresent application; and Ser. No. 11/165,683, entitled “MULTILAYEROPTICAL COMPENSATOR, LIQUID CRYSTAL DISPLAY AND PROCESS” and filed onthe same date as the present application are all incorporated herein byreference in their entireties as if fully set forth herein.

In the '109 application, a multilayer optical compensator is disclosedhaving at least one embodiment that is characterized by two or morefirst layers having an out-of-plane birefringence not more negative than−0.005, and one or more second layers having an out-of-planebirefringence more negative than −0.005, wherein the second layers areamorphous and comprise selected polymeric materials having sufficientthickness so that the overall in-plane retardation (R_(in)) of thecompensator is from 0 to 300 nm and the out-of-plane retardation(R_(th)) of at least one of the one or more second layers is morenegative than −20 nm wherein: (a) a first layer is present that iscontiguous to a second layer and is between all of the second layers andall of the other first layers; (b) at least one of the second layers orone of the other first layers is a layer coated from an organic solvent;and (c) the contiguous first layer contains a polymer that is watersoluble or water dispersible in an amount sufficient to impede thediffusion of the organic solvent between the other first layers and thesecond layers.

In various liquid crystal displays, it is desirable to modify thebirefringence of polarizer stack layers, to optimize the viewing anglefor the complete screen system. The manufacturing methods of embodimentsdisclosed herein, in combination with specific polymers, allow a basicsheet comprising one or more first polymeric layer, to be coated (orco-cast) with one or more second polymeric layers. The thickness of thefirst and the second layer polymers can be varied to provide a “tunable”package of optical properties. In dry-stretching, stresses applied tothe sheet after manufacturing can control the in-plane (x,y) retardationand the thickness of the second layer polymer can control theout-of-plane retardation. This can result in a simple way to create auseful sheet in a cost effective manner.

It has been found by the inventors that stretching (“active tentering”)of an already dried multilayer optical compensator can produce desirableamounts of in-plane anisotropy. In particular, by stretching an alreadydried multilayer optical compensator it is possible produce in-planeretardation values of up to 300 nm. Stretching can occur in a transversedirection, i.e., in a direction coincident with a casting direction ofthe film. Alternately, or in addition, stretching can occur in adirection perpendicular the transverse direction. Also alternately, orin addition, stretching can occur obliquely relative to the transversedirection (i.e. in a diagonal fashion).

It has also been found by the inventors that providing a barrier layerbetween the first layer(s) and the second layer(s) can preventdegradation to the optical properties of the first layer(s) that mayoccur during the process of coating the second layer(s) thereon, whileat the same time improving adhesion between the first and second layers.In particular, when the second layer is coated from an organic solvent,the provision of a barrier layer can prevent a substantial amount oforganic solvent(s) from permeating into the first layer(s). If allowedto permeate into the first layer(s), these organic solvents can degradethe optical characteristics of the multilayer optical compensator duringsubsequent process steps, such as heating the multilayer opticalcompensator during a stretching process.

Accordingly, disclosed herein are a class of multilayer opticalcompensators at least partially characterized by the provision of abarrier layer that contains a polymer that is water soluble or waterdispersible in an amount sufficient to impede the diffusion of theorganic solvent between the other first layers and the second layers.Also beneficially, the barrier layer comprises a stretchable materialsuch that the multilayer optical compensator can be stretched in atleast one direction by at least 1% and not more than 60% after at leasttwo of the first layers were assembled together.

Beneficially, in the case where the out-of-plane retardation (R_(th)) ofthe multilayer compensator is more negative than −20 nm, at least onesecond layer includes a polymer containing in the backbone a non-visiblechromophore group and has a T_(g) above 110° C. The non-visiblechromophore group may include a vinyl, carbonyl, amide, imide, ester,carbonate, aromatic, sulfone, or azo, phenyl, naphthyl, biphenyl,bisphenol, or thiophene group. Where the out-of-plane retardation of themultilayer compensator is more negative than −20 nm, the second layermay include a copolymer containing one or more of the following: (1) apoly(4,4′-hexafluoroisopropylidene-bisphenol)terephthalate-co-isophthalate, (2) apoly(4,4′-hexahydro-4,7-methanoindan-5-ylidene bisphenol) terephthalate,(3) a poly(4,4′-isopropylidene-2,2′6,6′-tetrachlorobisphenol)terephthalate-co-isophthalate, (4) apoly(4,4′-hexafluoroisopropylidene)-bisphenol-co-(2-norbornylidene)-bisphenolterephthalate, (5) apoly(4,4′-hexahydro-4,7-methanoindan-5-ylidene)-bisphenol-co-(4,4′-isopropylidene-2,2′,6,6′-tetrabromo)-bisphenolterephthalate, (6) apoly(4,4′-isopropylidene-bisphenol-co-4,4′-(2-norbornylidene)bisphenol)terephthalate-co-isophthalate, (7) apoly(4,4′-hexafluoroisopropylidene-bisphenol-co-4,4′-(2-norbornylidene)bisphenol)terephthalate-co-isophthalate, or (8) copolymers of any two or more ofthe foregoing

As an example of an undesirable approach for these compensators havingan R_(th) more negative than −20 nm, one would incorporate the fluorinegroup into the second layer polymer. This would introduce a non-visiblechromophore group(s) off of the backbone, which would “fight” thedesired non-visible chromophore group(s) in the backbone. While thefluorine group can enhance polymer solubility, one pays a high price indiminished out-of-plane birefringence with this approach (balancingnon-visible chromophore group(s) both in and off of the backbone).

In the case where the out-of-plane retardation of the multilayercompensator is more positive than +20 nm, at least one second layerincludes a polymer which contains off the backbone a non-visiblechromophore group and has a glass transition temperature (Tg) above 110°C. The non-visible chromophore group may include a carbonyl, amide,imide, ester, carbonate, phenyl, naphthyl, biphenyl, bisphenol, orthiophene group, or a heterocyclic or carbocyclic aromatic group. Thepolymer may contain off the backbone a vinyl, carbonyl, amide, imide,ester, carbonate, aromatic, sulfone, or azo group. Where theout-of-plane retardation of the multilayer compensator is more positivethan +20 nm, the second layer(s) may include one or more of thefollowing polymers: (A) poly(4 vinylphenol), (B) poly(4 vinylbiphenyl),(C) poly(N-vinylcarbazole), (D) poly(methylcarboxyphenylmethacrylamide),(E) poly[(1-acetylindazol-3-ylcarbonyloxy)ethylene], (F)poly(phthalimidoethylene), (G)poly(4-(1-hydroxy-1-methylpropyl)styrene), (H)poly(2-hydroxymethylstyrene), (1) poly(2-dimethylaminocarbonylstyrene),(J) poly(2-phenylaminocarbonylstyrene), (K)poly(3-(4-biphenylyl)styrene), (L) poly(4-(4-biphenylyl)styrene), (M)poly(4-cyanophenyl methacrylate), (N) poly(2,6-dichlorostyrene), (O)poly(perfluorostyrene), (P) poly(2,4-diisopropylstyrene), (O)poly(2,5-diisopropylstyrene), and (R) poly(2,4,6-trimethylstyrene), and(S) copolymers of any two or more of the foregoing

First layer materials are desirably suitable to be solvent cast orcoated such as TAC, other cellulose esters, polycarbonate, and cyclicpolyolefins.

The manufacture of TAC films is well known, including the followingprocess. A TAC solution (dope) can be prepared according to thefollowing conventional method. In the conventional method, theprocedures are conducted at a temperature of not less than 0° C. (roomtemperature or high temperature). The solution can be prepared by aknown dope preparation process with an apparatus used in a normalsolvent casting method. As the solvent, a halogenated hydrocarbon(particularly, methylene chloride) is typically used in this method. Theamount of TAC is so adjusted that the content of cellulose acetate in aprepared solution is in the range of 10 to 40 wt. %, and typically inthe range of 10 to 30 wt. %. Additives (described below) can be added tothe organic (main) solvent.

The dope is cast on a drum or a band, and the solvent is evaporated toform a film. Before casting the dope, the concentration of the dope istypically so adjusted that the solid content of the dope is in the rangeof 18 to 35 wt. %. The surface of the drum or band is typically polishedto give a mirror plane. The casting and drying stages of the solventcast methods are described in U.S. Pat. Nos. 2,336,310, 2,367,603,2,492,078, 2,492,977, 2,492,978, 2,607,704, 2,739,069, 2,739,070,British Patent Nos. 640,731, 736,892, Japanese Patent Publication Nos.45(1970)-4554, 49(1974)-5614, Japanese Patent Provisional PublicationNos. 60(1985)-176834, 60(1985)-203430 and 62(1987)-115035.

A plasticizer can be added to the cellulose acetate film to improve themechanical strength of the film. The plasticizer has another function ofshortening the time for the drying process. Phosphoric esters andcarboxylic esters (such as phthalic esters and citric esters) areusually used as the plasticizer. Examples of the phosphoric estersinclude triphenyl phosphate (TPP) and tricresyl phosphate (TCP).Examples of the phthalic esters include dimethyl phthalate (DMP),diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate(DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP).Examples of the citric esters include o-acetyltriethyl citrate (OACTE)and o-acetyltributyl citrate (OACTB).

Examples of the other carboxylic esters include butyl oleate,methylacetylricinoleate, dibutyl sebacate and various trimelliticesters. The plasticizers of phthalic esters (DMP, DEP, DBP, DOP, DPP,DEHP) are preferred, and DEP and DPP are particularly preferred. Theamount of the plasticizer is in the range of typically 0.1 to 25 wt. %,conveniently 1 to 20 wt. %, and desirably 3 to 15 wt. % based on theamount of cellulose acetate.

Stabilizers (e.g., oxidation inhibitor, peroxide decomposer, radicalinhibitor, metal inactivating agent, oxygen scavenger, amine) can bealso incorporated into the cellulose acetate film. The stabilizers aredescribed in Japanese Patent Provisional Publication Nos.3(1991)-199201, 5(1993)-1907073, 5(1993)-194789, 5(1993)-271471 and6(1994)-107854. The amount of the deterioration inhibitor is in therange of 0.01 to 1 wt. %, and typically 0.01 to 0.2 wt. % based on theamount of the solution (dope). If the amount is less than 0.01 wt. %,the deterioration inhibitor hardly gives the effect. On the other hand,if the amount is more than 1 wt. %, the deterioration inhibitor oftenbleeds out onto the film surface. Examples of particularly preferreddeterioration inhibitors include butyrated hydroxytoluene (BHT) andtribenzylamine (TBA).

Organic solvents are liquids other than water. Typically these wouldinclude aromatic or alkyl hydrocarbons, alcohols, esters, ketones,aldehydes, and halogenated analogues of the preceding list. Convenientlythese would include methylacetate, ethylacetate, propylacetate,butylacetate, acetone, methylethylketone, toluene, xylene,cycopentanone, cyclohexanone, and methylene chloride. Mixtures of theabove organic solvents may also prove useful. Such organic solvents mayremain in the layers of the compensator. The amount retained in thecompensator would depend on such factors as vapor pressure of thesolvent, appropriate diffusion constants, layer thickness, temperature,and duration of drying. These residual amounts of such organic solventscould be detected by techniques such as head-space gas chromatography ata minimum detection level of about 5 mg/ft².

The thickness of the TAC film is less than 140 μm, typically in therange of 70 to 115 μm, and desirably from 40 to 100 μm.

In the case that the cellulose acetate film is used as a transparentprotective film of a polarizing plate, the film surface is typicallysubjected to a surface treatment. Examples of the surface treatmentsinclude a corona discharge treatment, a glow discharge treatment, aflame treatment, an acid treatment, an alkali treatment and anultraviolet ray irradiating treatment. The acid treatment or the alkalitreatment is preferred. The acid treatment or the alkali treatment canfunction as a saponification treatment to the cellulose acetate film.

The alkali treatment is particularly preferred. The alkali treatmentuses an aqueous alkali solution. The alkali typically is hydroxide of analkali metal, such as sodium hydroxide or potassium hydroxide. Theaqueous alkali solution has a pH value of typically higher than 10. Atleast one surface of the cellulose acetate film is immersed in theaqueous alkali solution typically for 1 to 300 seconds, and desirablyfor 5 to 240 seconds. The alkali treatment is conducted typically at 25to 70° C., and desirably at 35 to 60° C. After the alkali treatment, thecellulose acetate film is typically washed with water.

First layer films as made by the above process will typically have inplane retardation (R_(in)) values of 0 to 5 nm. To generate greateramounts of R_(in) (>5 nm) in the first layer, any viable methods can beused, however, the most commonly practiced approach is stretching. Whena polymer is stretched, individual polymer chain segments are orientedpredominantly to the direction of primary stretch, thus increase the inplane birefringence of the polymer layer. This is typically done abovethe glass transition temperature (Tg) of the polymer. Thus, thepolymeric film is heated above Tg and stretched. As noted in thebackground section, certain small molecules can be added to a stretchedfilm to enhance R_(in). The first film can be stretched uniaxially orbiaxially. In uniaxial stretching, the film is stretched in onedirection. In biaxial stretching, the two stretching directions aretypically perpendicular to each other. The first layer has out of planebirefringence not more negative than −0.005 and not more positive that+0.005, and the first layer of the multilayer compensator is such thatthe overall in-plane retardation (R_(in)) of the multilayer compensatorcan be between 0 and 300 nm.

In the embodiments disclosed herein, a first layer that is contiguous toa second layer and that is between all second layers and all of theother first layers, is a barrier layer that inhibits the diffusion oforganic solvents between the second layer(s) and the other firstlayer(s). The barrier layer will typically be applied to a first layersuch as a TAC film as described hereinabove.

In order to optimize both barrier properties and adhesion to contiguouslayers, the barrier layer typically will contain two or more polymers.For example, the barrier layer may contain a water-soluble polymer suchas polyvinyl alcohol and a water dispersible polymer such as apolyesterionomer.

Alternatively, the barrier layer may contain two different waterdispersible polymers such as a polyesterionomer and a polyurethane.

The barrier layer may be crosslinked using known methods such as theaddition of crosslinking agents, such at isocyanates, aldehydes, vinylsulfone materials, aziridines and melamine resins or by exposure of thedried layer to actinic radiation.

The barrier layer is generally applied at dried coating weights between10 and 6000 mg/ft², more typically between 50 and 1000 mg/ft². Barrierlayer dried coating weights less than 10 mg/ft² are insufficient toprevent the diffusion of organic solvents from subsequent layers frompenetrating other first layers such as TAC film.

Addenda such as surfactants or rheology modifiers may be added to thebarrier layer to improve coating quality, adhesion and other propertiesof the layer.

The second layer(s) can be coated from a solution containing a polymerthat yields high positive or negative out of plane birefringence uponsolvent coating. To produce negative out-of-plane birefringence(negative out of plane retardation), polymers that contain non-visiblechromophore groups such as vinyl, carbonyl, amide, imide, ester,carbonate, sulfone, azo, and aromatic groups (i.e. benzene, naphthalate,biphenyl, bisphenol A) in the polymer backbone will be used, such aspolyesters, polycarbonates, polyimides, polyetherimides, andpolythiophenes. To produce positive out-of-plane birefringence (negativeout of plane retardation), polymers that contain off the backbone avinyl, carbonyl, amide, imide, ester, carbonate, aromatic, sulfone, orazo group, will be used, such as a carbonyl, amide, imide, ester,carbonate, phenyl, naphthyl, biphenyl, bisphenol, or thiophene group, aheterocyclic or carbocyclic aromatic group. One could also add fillersand non-polymeric molecules to this second layer.

Other suitable second layer materials include polyimides such as:

poly(ether ketones) and poly(ether ether ketones) such as:

The polymers used in the second layer could be synthesized by a varietyof techniques: condensation, addition, anionic, cationic or other commonmethods of synthesis could be employed.

The thickness of this second layer should be less than 30 μm. Typicallyit should be from 0.1 μm to 20 μm. Conveniently it should be from 1.0 μmto 10 μm. Desirably it should be from 2 μm to 8 μm.

The formulations for the barrier layer and second layer(s) describedherein can be coated by various coating procedures including wire woundrod coating, dip coating, air knife coating, curtain coating, slidecoating, or extrusion coating using hoppers of the type described inU.S. Pat. No. 2,681,294 (Beguin). Layers can be coated one at a time, ortwo or more layers can be coated simultaneously by the proceduresdescribed in U.S. Pat. No. 2,761,417 and U.S. Pat. No. 2,761,791(Russell), U.S. Pat. No. 4,001,024 (Dittman et al.), U.S. Pat. No.4,569,863 (Keopke et al.), U.S. Pat. No. 5,340,613 (Hanzalik et al.),U.S. Pat. No. 5,405,740 (LaBelle), U.S. Pat. No. 5,415,993 (Hanzalik etal.), U.S. Pat. No. 5,525,376 (Leonard), U.S. Pat. No. 5,733,608 (Kesselet al.), U.S. Pat. No. 5,849,363 (Yapel et al.), U.S. Pat. No. 5,843,530(Jerry et al.). The coated layers can be dried in forced air at atemperature of from about 20° C. to about 115° C.

The combined thickness of the multilayer compensator should be less than180 μm. Typically it should be from 41 μm to 105 μm. Desirably it shouldbe from 41 μm to 90 μm.

The second layer should be of sufficient thickness so that theout-of-plane retardation of the multilayer compensator is more negativethan −20 nm or more positive than +20 nm. Beneficially, it should befrom −600 nm to −40 nm, or from +600 nm to +40 nm. More beneficially, itshould be from −500 nm to −60 nm, or from +500 nm to +60 nm. Desirablyit should be from −400 nm to −80 nm, or from +400 nm to +80 nm.

Also disclosed is a method for forming a compensator polymeric film.

Various aspects of the embodiments disclosed herein can be seen ingreater detail by referring to the drawings as follows.

FIG. 1 shows a cross-sectional schematic of a multilayer compensator 5.The compensator includes a polymeric first layer 10, a contiguous firstlayer 15 that also serves as a barrier layer, and a polymeric secondlayer 20 that is contiguous to the barrier layer 15, and the combinedin-plane retardation (R_(in)) of layers 10, 15 and 20 is from 0 to 300nm and the out-of-plane retardation (R_(th)) of multilayer compensator 5is more negative than −20 nm or more positive than +20 nm.

FIG. 2 shows a cross-sectional schematic of another multilayercompensator 6. The compensator includes a polymeric first layer 10, acontiguous layer 15 that also serves as a barrier layer, a polymericsecond layer 20, another contiguous first layer 25 that also serves as abarrier layer, and another polymeric second layer 30, wherein barrierlayer 15 is contiguous to layers 10 and 20 and barrier layer 25 iscontiguous to layers 20 and 30, and the combined in-plane retardation(R_(in)) of the layers 10, 15, 20, 25 and 30 is from 0 to 300 nm and theout-of-plane retardation (R_(th)) of the multilayer compensator 6 ismore negative than −20 nm or more positive than +20 nm. The compositionof layers 10 and 30 may or may not be the same. Also, the composition ofbarrier layers 15 and 25 may or may not be the same.

FIG. 3 shows a cross-sectional schematic of another multilayercompensator 7. The compensator includes a polymeric first layer 10, acontiguous first layer 15 that also serves as a barrier layer, apolymeric second layer 20, another contiguous first layer 25 that alsoserves as a barrier layer, and another polymeric second layer 40,wherein barrier layer 15 is contiguous to layers 10 and 20 and barrierlayer 25 is contiguous to layers 10 and 40, and the combined in-planeretardation (R_(in)) of the layers 10, 15, 20, 25 and 40 is from 0 to300 nm and the combined out-of-plane retardation (R_(th)) of themultilayer compensator 7 is more negative than −20 nm or more positivethan +20 nm. The composition of layers 20 and 40 may or may not be thesame. Also, the composition of barrier layers 15 and 25 may or may notbe the same. Conveniently, layers 20 and 40 have the same compositionand thickness in order to provide a symmetrical multilayer compensator.One skilled in the art could conceive of more complex structures.

FIG. 4A shows a schematic liquid crystal display 700 where 300 is asingle compensating film is placed on one side of the liquid crystalcell 600. 500 is a polarizer, and 550 is a second polarizer. Thetransmission axes for the polarizers 500 and 550 form a 90°±10° anglerelative to each other. The angles of their transmission axes aredenoted as 0° and 90° relative to the liquid crystal cell 600. However,other angles are possible depending on the kind of liquid crystaldisplay 700 and this is obvious to those who skilled in the art. Notethat 600 is the electrically switchable liquid crystal cell with theliquid crystals confined between two glass plates.

FIG. 4B shows another schematic liquid crystal display 700 where thereare two compensating films 300 placed on both sides of the liquidcrystal cell (600). 500 is a polarizer and 550 is a second polarizer.The transmission axes for the polarizers 500 and 550 form a 90°±0° anglerelative to each other. The angles of their transmission axes aredenoted as 0° and 90° relative to the liquid crystal cell 600. However,other angles are possible depending on the kind of liquid crystaldisplay 700 and this is obvious to those who skilled in the art. Notethat 600 is the electrically switchable liquid crystal cell with theliquid crystals confined between two glass plates.

Compared to the prior art, embodiments disclosed herein do not requirethe use of expensive liquid crystal molecules, do not require filmlamination (thus reducing the chance introduction of dirt or unwantedoptical retardation from the laminating adhesive), provide enhancedoptical compensation in a relatively thin (<115 um) structure, and areeasily manufactured. As a further attribute, embodiments enable thecontrol of R_(in) which is primarily the responsibility of the firstlayer while control of R_(th) is primarily the responsibility of thesecond layer. In the prior art, R_(in) and R_(th) are often coupled andare not controlled independently. Embodiments disclosed herein alsoprovide a compensator having excellent adhesion between layers and thatis substantially free of organic solvent-induced curl.

The present invention is further illustrated by the followingnon-limiting examples of its practice.

In the experiments as explained in more detail below, 80 μm of triacetyl cellulose (TAC) (typically 2.86 acetyl substitution, 220,000 M.W.polymer) was produced via a solvent casting process with appropriateaddenda. One or more layers of water soluble or water dispersiblepolymeric materials were coated, from an aqueous mixture, onto a TACfilm. In each case, these materials comprised one or more of thematerials listed in Table A below (the source of each material is listedin parentheses). B-7 polymer was prepared by the following procedure. 19kg of deionized water was added to a glass-lined reactor, and 18 kg ofdeionized water was added to a glass-lined head tank. 932 g of RHODACAL®A246L (Rhodia) was rinsed into the reactor with 1 kg of deionized water,and the reactor temperature was set to 60° C. To the head tank 15.9 kgof glycidyl methacrylate, 2.8 kg of butyl acrylate, and 932 g ofRHODACAL® A246L was rinsed in with 1 kg of deionized water. To themonomer emulsion 187 g of azobis(4-cyano)valeric acid (75%) was added tothe reactor. Within two minutes the monomer emulsion addition, into thereactor, was started (310 mL/minute). When the monomer addition wascomplete the head tank was rinsed with 2 kg of deionized water. Thereactor contents were stirred for two hours at 60° C. 226 g of (35%)hydrogen peroxide was added to a dropping funnel. To the reactor, 80 gof erythobic acid was added, which was dissolved in 1 kg of deionizedwater. Within two minutes the hydrogen peroxide addition from thedropping funnel began, when the addition was complete the flask wasrinsed with 1 kg of deionized water. The glycidyl methacrylate butylacrylate (85:15) copolymer latex was cooled to 25° C., the yield was 68kg at 30% solids.

TABLE A B-1 SANCURE ® 898 (Noveon) B-2 EASTEK ® 1100 Alcohol-Free(Eastman) B-3 AQ ® 29D (Eastman) B-4 NEOREZ ® R-966 (DSM) B-5WITCOBOND ® 240 (Crompton) B-6 WITCOBOND ® 242 (Crompton) B-7 Glycidylmethacrylate n-butyl acrylate copolymer B-8 ELVANOL ® 52-22 (Dupont) B-9CELVOL ® 103 (Celanese) B-10 CELVOL ® 107 (Celanese) B-11 CELVOL ® 205(Celanese) B-12 CELVOL ® 603 (Celanese)

Examples of single layer coatings are listed in Table B. Compositionsalso include mixtures of water dispersible polymeric materials.

TABLE B Barrier Layer Barrier Layer Ratio of Thickness ExampleComposition components (μm) 1 B-1 + B-2 1:1 0.1 2 B-1 + B-2 1:1 0.8 3B-1 + B-2 1:1 2.2 4 B-1 + B-2 1:1 3.2 5 B-1 + B-2 1:1 4.2 6 B-1 + B-21:0.43 3.6 7 B-4 + B-2 1:0.43 3.9 8 B-8 — 0.6 9 B-9 — 0.7 10 B-12 + B-21:0.43 1.0 11 B-11 + B-2 1:0.43 1.0Multi-layer layer coatings of water soluble or water dispersible barriermaterials, coated simultaneously, are listed in Table C. Layer Xcorresponds to the bottom-most layer, layer Y the middle layer, andlayer Z the topmost layer, as coated onto a TAC support. The totalmulti-layer thickness corresponds to a combined total of all threelayers.

TABLE C Ratio of Total Multi- Barrier Barrier Layer Y Barrier layerthickness Example Layer X Layer Y components Layer Z (μm) 12 B-3 B-1 +B-2 1:1 B-3 4.1 13 B-3 B-1 + B-2 1:1 B-7 4.6 14 B-3 B-1 + B-2 1:1 B-54.2 15 B-3 B-1 + B-2 1:1 B-6 5.0 16 B-3 B-9 — B-6 1.9 17 B-3 B-9 — B-52.3 18 B-3 B-9 — B-7 1.8Various known cross-linking additives were mixed with single barrierlayer compositions prior to coating, described in Table D. The weight %is the amount of additive based on the total polymer concentration inthe coating mixture. CX-100 is a polyaziridine, Cymel 373 is a partiallymethylated melamine resin.

TABLE D Barrier Barrier Layer(s) Layer wt ratio wt % of ThicknessExample Composition of components cross-linker (μm) 19 B-1 + B-2 1:0.430.4 CX-100 3.4 (DSM) 20 B-4 + B-2 1:0.43 0.4 CX-100 3.4 (DSM) 21 B-8 —0.5 Cymel 373 0.5 (Cytec)

After drying, a birefringent amorphous polyester polymer layer wasfurther coated on the films of Examples 1–21, using conventional coatingmethods. The polymer(poly(4,4′-hexafluoroisopropylidene-bisphenol-co-4,4′-(2-norbornylidene)bisphenol)terephthalate-co-isophthalate)was dissolved in a mixture of 90% ethylacetate and 10% propylacetate,coated, and dried. The residual solvent (ethylacetate and propylacetate)remaining in the film was measured 1–2 after coating by gas chromatogram(Table E). Example 1 is of the thinnest barrier coating, which resultedin an elevated level of retained solvent in the film.

TABLE E Second Layer Thickness Ethylacetate Propylacetate Example (μm)(mg/ft²) (mg/ft²) 1 5.0 72 104 2 4.4 18 63 3 4.5 11 54 4 4.5 12 54 5 4.45 34 6 3.1 8 17 7 3.6 39 60 8 3.3 1 19 9 3.2 2 19 10 3.2 3 13 11 3.2 415 12 3.4 4 <1 13 3.5 4 <1 14 3.7 7 <1 15 4.0 <1 <1 16 3.4 4 <1 17 3.4 4<1 18 3.5 5 <1 19 3.3 3 22 20 3.6 41 64 21 3.2 4 14

The composite films were then stretched uniaxially on a film stretcherusing a uniaxial constrained mode. In this mode the film was held inboth directions, heated to a temperature and stretched in one of theheld directions to a desired stretch ratio. The composite film was thencooled to room temperature before the tension was removed. The in-plane(R_(in)) and out-of-plane (R_(th)) retardations were measured, at awavelength of 590 nm, using the M-2000V Spectroscopic Ellipsometer (J.A. WOOLLAM CO.®). The haze was measured using a Haze-gard Plus (BYKGARDNER®) according to ASTM D-1003 and ASTM D10044 standards. Theconditions used to prepare the exemplary composite films, the multilayercompensator in-plane (R_(in)), out-of-plane (R_(th)) retardation values,corresponding second layer birefringence, and haze are listed in Table Fbelow.

TABLE F Birefrin- Stretch gence of Haze after Temperature Stretch Secondstretching Example (° C.) Ratio Layer Rin Rth (%) 1 141 1.15 −0.021 47−158 2.0 2 141 1.15 −0.028 53 −176 1.2 3 141 1.15 −0.027 52 −173 1.0 4141 1.15 −0.027 54 −175 1.0 5 141 1.15 −0.029 53 −182 0.9 6 140 1.2−0.036 52 −164 0.9 7 142 1.2 −0.025 49 −142 1.1 8 140 1.2 −0.039 60 −1811.0 9 140 1.2 −0.043 63 −190 1.1 10 142 1.2 −0.031 49 −152 1.2 11 1401.2 −0.030 48 −150 2.0 12 145 1.2 −0.063 37 −218 1.1 13 145 1.2 −0.06034 −214 1.3 14 145 1.2 −0.056 29 −211 1.0 15 145 1.2 −0.049 29 −205 1.116 145 1.2 −0.055 29 −194 1.4 17 145 1.2 −0.062 29 −217 1.2 18 145 1.2−0.065 36 −233 2.3 19 140 1.2 −0.037 59 −178 0.7 20 140 1.2 −0.027 50−148 0.9 21 140 1.2 −0.031 47 −152 1.7

The out of plane retardation (R_(th)) contribution from an 80 μm TACsheet varies from approximately −80 nm to a value of about −40 nm. TheTAC R_(th) can be manipulated by changes in the TAC casting process andthe multilayered compensator stretching process.

In similarity to previous examples 1–21, a single layer barrier wascoated onto 80 μm thickness TAC support and dried. After drying, abirefringent second layer was further coated on the above-coated filmusing an amorphous polymer comprising a polycarbonate (PC). The PCpolymers were dissolved in methylene chloride. Specific layerthicknesses and compositions are shown in Table G. A coating of PCwithout a barrier layer is included for comparison. Examples with abarrier layer result in significantly lower residual methylene chloridein the coating (as measured by gas chromatograph).

TABLE G Barrier Birefringent Residual Barrier Layer Layer MethyleneLayer Thickness Thickness chloride Example Composition (μm) (μm)Birefringent Layer (mg/ft²) Comparison None 0 7.3 LEXAN ® 131-112(GE)1018 22 B-9 1.0 6.1 LEXAN ® 141-112(GE) 121 23 B-10 1.0 6.2 LEXAN ®141-112 135 24 B-9 1.8 6.1 LEXAN ® 131-112 145The composite films were then stretched uniaxially on a film stretcherusing a uniaxial constrained mode and retardation measurements performedsimilar to Examples 1–21.

TABLE H Stretch Birefringence Haze after Temperature Stretch of theSecond stretching Example (° C.) Ratio Layer Rin Rth (%) Comparison 1551.3 −0.001 29 −62 1.0 22 155 1.3 −0.006 32 −92 1.1 23 155 1.3 −0.006 33−91 1.4 24 155 1.3 −0.009 46 −108 1.3

Multilayer compensators including at least two polymeric first layers(including a barrier layer), and one or more polymeric second layers, asdisclosed herein may be fabricated under several scenarios.

According to a first scenario, one first layer (e.g., a TAC layer) isunwound, and another first layer (e.g., a barrier layer) is coatedthereon. The resultant film is then stretched before one or more secondlayers is/are coated thereon.

According to a second scenario, one first layer (e.g., a TAC layer) isunwound, and another first layer (e.g., a barrier layer) is coatedthereon. One or more second layers is/are coated on the combined firstlayers, and the resultant product including the two first layers and theone or more second layers is stretched.

In these scenarios, the temperature Ts at which stretching is performedbeneficially satisfies one of the following relationships: (1) Ts isgreater than or equal to the Tg of both first layers and the secondlayer(s); (2) Ts is greater than the Tg of both first layers and thesecond layer(s); (3) Ts is greater than the Tg of both first layers, butless than the Tg of the second layer(s); or (4) Ts is greater than theTg of both first layers, but much less than the Tg of the secondlayer(s). Other arrangements are possible.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be affected within the scope of theinvention.

PARTS LIST

-   5 compensator according to one embodiment of the present invention-   6 compensator according to one embodiment of the present invention-   7 compensator according to one embodiment of the present invention-   10 polymeric first layer-   15 contiguous first layer that serves as a barrier-   20 polymeric second layer-   25 contiguous first layer that serves as a barrier-   30 polymeric second layer-   40 polymeric second layer-   300 compensator according to one embodiment of the present invention-   500 polarizer-   550 polarizer-   600 liquid crystal cell-   700 liquid crystal display

1. A multilayer compensator comprising: at least two polymeric firstlayers; and one or more polymeric second layers, wherein the firstlayers comprise a polymer having an out-of-plane birefringence not morenegative than −0.005 and not more positive than +0.005; wherein thesecond layers comprise a polymer having an out-of-plane birefringencemore negative than −0.005 or more positive than +0.005; wherein theoverall magnitude of the in-plane retardation (R_(in)) of the multilayercompensator is greater than 0 nm and less than 300 nm and theout-of-plane retardation (R_(th)) of the multilayer compensator is morenegative than −20 nm or more positive than +20 nm, wherein one of thefirst layers is contiguous to a second layer and is between all of theother first layers and all of the second layers, wherein at least one ofthe second layers is a layer coated from an organic solvent, wherein thecontiguous first layer includes a polymer that is water soluble or waterdispersible in an amount sufficient to limit an amount of the organicsolvent that diffuses into the first layers to be less than 75 mg/ft²when the organic solvent is ethylacetate, less than 105 mg/ft² when theorganic solvent is propylacetate, and less than 150 mg/ft² when theorganic solvent is methylene chloride, and wherein the compensator hasbeen stretched in at least one direction by at least 1% and not morethan 60% after at least two of the first layers were assembled together.2. The multilayer compensator of claim 1, wherein the compensator hasbeen stretched at least 10% and not more than 60%.
 3. The multilayercompensator of claim 1, wherein the compensator has been stretched atleast 12% and not more than 60%.
 4. The multilayer compensator of claim1, wherein the compensator has been stretched at least 20% and not morethan 60%.
 5. The multilayer compensator of claim 1, wherein at least twoof the layers are contiguous layers.
 6. The multilayer compensator ofclaim 1, wherein all of said first and said second layers arecontiguous.
 7. The multilayer compensator of claim 1, wherein the secondlayers have a combined thickness of less than 30 micrometers.
 8. Themultilayer compensator of claim 1, wherein the second layers have acombined thickness of from 1.0 to 10 micrometers.
 9. The multilayercompensator of claim 1, wherein the second layers have a combinedthickness of from 2 to 8 micrometers.
 10. The multilayer compensator ofclaim 1, wherein the overall in-plane retardation (R_(in)) of saidmultilayer compensator is between 21 and 200 nm.
 11. The multilayercompensator of claim 1, wherein the overall in-plane retardation(R_(in)) of said multilayer compensator is between 25 and 150 nm. 12.The multilayer compensator of claim 1, wherein the overall in-planeretardation (R_(in)) of said multilayer compensator is between 25 and100 nm.
 13. The multilayer compensator of claim 1, wherein the combinedthickness of the first and second layers is less than 180 μm.
 14. Themultilayer compensator of claim 1, wherein the combined thickness of thefirst and second layers is from 41 to 105 μm.
 15. The multilayercompensator of claim 1, wherein the combined thickness of the first andsecond layers is from 41 to 90 μm.
 16. The multilayer compensator ofclaim 1, wherein the polymer of the one or more second layers is anamorphous polymer.
 17. The multilayer compensator of claim 1, whereinthe contiguous first layer includes a polymer that is water soluble orwater dispersible in an amount sufficient to limit an amount of theorganic solvent that diffuses into the first layers to be less than 45mg/ft² when the organic solvent is ethylacetate, and less than 65 mg/ft²when the organic solvent is propylacetate.
 18. The multilayercompensator of claim 1, wherein the out-of-plane retardation (R_(th)) ofthe multilayer compensator is more negative than −20 nm.
 19. Themultilayer compensator of claim 18, wherein the polymer of the one ormore second layers contains in the backbone a non-visible chromophoregroup and has a glass transition temperature (Tg) greater than 110° C.20. The multilayer compensator of claim 19, wherein the polymer of theone or more second layers comprises pendant cycloaliphatic groups. 21.The multilayer compensator of claim 20, wherein the cycloaliphaticgroups are at least one selected from the group of cyclopentane,cyclohexane, norbornene, hexahydro-4,7-methanoindan-5-ylidene,adamantane, and any of the forgoing having fluorine substitution for atleast one hydrogen atom.
 22. The multilayer compensator of claim 18,wherein the polymer of the one or more second layers contains in thebackbone a nonvisible chromophore containing a vinyl, carbonyl, amide,imide, ester, carbonate, aromatic, sulfone, or azo, phenyl, naphthyl,biphenyl, bisphenol, or thiophene group.
 23. The multilayer compensatorof claim 18, wherein the polymer of the one or more second layerscomprises a copolymer containing (1) apoly(4,4′-hexafluoroisopropylidene-bisphenol)terephthalate-co-isophthalate, (2) apoly(4,4′-hexahydro-4,7-methanoindan-5-ylidene bisphenol) terephthalate,(3) a poly(4,4′-isopropylidene-2,2′6,6′-tetrachlorobisphenol)terephthalate-co-isophthalate, (4) apoly(4,4′-hexafluoroisopropylidene)-bisphenol-co-(2-norbornylidene)-bisphenolterephthalate, (5) apoly(4,4′-hexahydro-4,7-methanoindan-5-ylidene)-bisphenol-co-(4,4′-isopropylidene-2,2′,6,6′-tetrabromo)-bisphenolterephthalate, (6) apoly(4,4′-isopropylidene-bisphenol-co-4,4′-(2-norbornylidene)bisphenol)terephthalate-co-isophthalate, (7) apoly(4,4′-hexafluoroisopropylidene-bisphenol-co-4,4′-(2-norbornylidene)bisphenol)terephthalate-co-isophthalate, or (8) copolymers of any two or more ofthe foregoing.
 24. The multilayer compensator of claim 18, wherein thepolymer of the at least two first layers comprises a cellulosic,acrylic, cyclic polyolefin, or polyarylate containing flourene groups.25. The multilayer compensator of claim 1 wherein the out-of-planeretardation (R_(th)) of the multilayer compensator is more positive than+20 nm.
 26. The multilayer compensator of claim 25, the polymer of theone or more second layers contains off the backbone a vinyl, carbonyl,amide, imide, ester, carbonate, aromatic, sulfone, or azo group.
 27. Themultilayer compensator of claim 25, wherein the polymer of the one ormore second layers contains off the backbone a non-visible chromophoregroup and has a glass transition temperature (Tg) greater than 110° C.28. The multilayer compensator of claim 27, wherein the non-visiblechromophore group includes a carbonyl, amide, imide, ester, carbonate,phenyl, naphthyl, biphenyl, bisphenol, or thiophene group.
 29. Themultilayer compensator of claim 27, wherein the non-visible chromophoregroup includes a heterocyclic or carbocyclic aromatic group.
 30. Themultilayer compensator of claim 25, wherein the polymer of the one ormore second layers is selected from the group consisting of (A) poly(4vinylphenol), (B) poly(4 vinylbiphenyl), (C) poly(N-vinylcarbazole), (D)poly(methylcarboxyphenylmethacrylamide), (E)poly[(1-acetylindazol-3-ylcarbonyloxy)ethylene], (F)poly(phthalimidoethylene), (G)poly(4-(1-hydroxy-1-methylpropyl)styrene), (H)poly(2-hydroxymethylstyrene), (I) poly(2-dimethylaminocarbonylstyrene),(J) poly(2-phenylaminocarbonylstyrene), (K)poly(3-(4-biphenylyl)styrene), (L) poly(4-(4-biphenylyl)styrene), (M)poly(4-cyanophenyl methacrylate), (N) poly(2,6-dichlorostyrene), (O)poly(perfluorostyrene), (P) poly(2,4-diisopropylstyrene), (O)poly(2,5-diisopropylstyrene), (R) poly(2,4,6-trimethylstyrene), and (S)copolymers of any two or more of the foregoing.
 31. The multilayercompensator of claim 25, wherein the polymer of the at least two firstlayers comprises a cellulosic, acrylic, cyclic polyolefin, orpolyarylate containing flourene groups.
 32. The multilayer compensatorof claim 31, wherein the polymer of the at least two first layerscomprises triacetylcellulose, cellulose diacetate, cellulose acetatebutyrate, polycarbonate, cyclic polyolefin, polystyrene or polyarylatecontaining fluorene groups.
 33. A liquid crystal display comprising aliquid crystal cell, a pair of crossed polarizers located one on eachside of the cell, and at least one compensator of claim
 1. 34. Theliquid crystal display of claim 33, wherein said liquid crystal cell isa vertically aligned cell, a twisted nematic cell, an in-plane switchingmode cell, or an optically compensated bend liquid crystal cell.
 35. Aliquid crystal display comprising a liquid crystal cell, at least onepolarizer, a reflective plate, and at least one compensator of claim 1.36. The multiplayer compensator of claim 1 wherein the compensator hasbeen stretched in at least one direction by at least 1% and not morethan 60% after at least two of the first layers, including thecontiguous layer, were assembled together.